1. Field of the Invention
This invention relates to a heat-sensitive transferring recording medium.
2. Description of the Prior Art
The heat-sensitive transferring recording system has many advantages as compared with prior art impact type recording systems, that is, the heat-sensitive transferring recording system can make a noiseless printing, the printed letters are clear, of high quality, and highly durable. Therefore, the heat-sensitive transferring recording system has been recently developed to a great extent and is now used for printer, typewriters and the like.
The base material of the heat-sensitive transferring recording medium was paper in the prior art, but since paper has poor humidity resistance and gives poor sharpness of printed letter, there have been recently used film bases, in particular, PET (polyethylene telephthalate) film, mainly. Among various films, PET has a relatively high melting point. However, the surface temperature of thermal head upon printing reaches instantly 300.degree. C. or higher and therefore, so-called "stick" phenomenon is liable to occur, that is, PET film is partly melted and fused to the thermal head resulting in disturbing conveyance of the film, and at the worst, running of the film completely stops to make printing impossible.
In order to improve the film conveyance, there has been tried to apply silicone or paraffin to the surface of the film or to form a heat resistant thermosetting resin layer such as urethane resin layer, expoxy resin layer and the like on the surface of the film.
However, such countermeasures can not sufficiently prevent "stick", or require a long time heat treatment at high temperatures so as to cause the curing reaction and therefore, the working efficiency is very poor and the countermeasures can not be practically used.
In addition, even when the stick preventing effect is sufficient, if film-shapeability of the coating material and adhesivity to the PET surface are poor, the coated material falls off due to rubbing with thermal head and deposits on the thermal head portion results in formation of poor printed letters.
Other prior art method for improving the conveyance property is to use silicone resin, melamine resin or similar thermosetting resins for heat-sensitive paper and heat-sensitive transferring recording members, but this method involves chemical reactions, which are laborious, and further when coated therewith, the resulting recording medium is suffering from curling.